Exhaust gas recirculation (EGR) may be used in engines to decrease emissions (e.g., nitrogen oxide emissions), improve knock tolerances, improve combustion efficiency, and reduce throttling losses. EGR may be employed in engines utilizing compression or spark ignition. EGR system may flow exhaust gas from one or more of the cylinders in the engine to the engine's intake system via an EGR conduit. EGR valves may be disposed in EGR conduits to regulate exhaust gas flow through the conduits.
US 2012/0260897 discloses an EGR system having two dedicated EGR cylinders, each cylinder having two exhaust valves configured to flow exhaust gas to an EGR conduit or an exhaust treatment device in the exhaust system based on the configuration of valve assemblies positioned in conduits coupling the cylinders to the EGR and exhaust system. Specifically, the EGR system employs three external valve assemblies to regulate the exhaust flow to the EGR system and the exhaust system.
The Inventors have recognized several drawbacks with the EGR system disclosed in US 2012/0260897. For example, the valve assemblies may be susceptible to thermal degradation from the high temperature exhaust gases flowing therethrough. Additionally, the EGR valves may be costly, thereby increasing the engine's cost. Moreover, the valve assemblies may increase losses in the EGR conduit as well as the exhaust system, while the exhaust conduits themselves decrease the compactness of the engine.
The inventors herein have recognized the above issues and developed an engine that includes an exhaust gas recirculation (EGR) conduit in fluidic communication between a first exhaust valve in a cylinder and an intake system, and an exhaust conduit in fluidic communication between a second exhaust valve in the cylinder and an emission control device. The engine may further include a valve adjustment system, such as a first cam profile (CPS) system, to selectively activate the first exhaust valve and the second exhaust valve.
In this way, the valve adjustment system may be used to adjust the amount of EGR delivered to the intake system and the amount of exhaust gas delivered to the exhaust system from a single cylinder via dedicated cylinder valves and conduits. As a result, combustion efficiency may be improved and emission (e.g., nitrogen oxide emissions) may be reduced, without a complicated network of exhaust throttles (although exhaust throttles could be added, if desired).
In one example, a first CPS device activates valve operation of the first exhaust valve during a first condition and inhibits valve operation of the first exhaust valve during a second condition. Additionally, a second CPS device activates valve operation of the second exhaust valve during the second condition and inhibits valve operation of the second exhaust valve during the first operating condition. In this way, substantially all of the exhaust gas from the cylinder may be flowed to the EGR conduit during the first condition and flowed to the emission control device during the second condition. The first condition may be when the engine is below a threshold temperature. As a result, the emission control device may reach a light-off temperature more quickly. The first condition may also allow for improved peak engine performance by diverting the exhaust enthalpy of that cylinder to the turbocharger turbine. In the second condition, the exhaust from that cylinder is routed to the intake manifold as EGR, improving fuel economy via improved combustion efficiency, reduced pumping losses and reduced knock tendency. In an alternative embodiment, a single cam switching device can control activation/deactivation of both the first and second valves, together.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. Additionally, the above issues have been recognized by the inventors herein, and are not admitted to be known.